Congestion Avoidance with Future-Path Information

AbstractIn this paper we analyze the trade-off between admission costs and receiver rewardsof TCP Tahoe flows competing for buffer space. Since the buffer space is a scarce re-source during heavy traffic and congestion epochs, it is important to understand inwhich circumstances packet dropping may be optimal. We develop a restless banditmodel for assessing an economic value of packets at routers they encounter in transmit.We then argue that the economic value of the whole network increases if the packetswith lower economic value are the preferred candidates for dropping or marking incongestion avoidance mechanisms. Such changes are arguably expected to lead bothto a lower delay and higher network throughput.Key Words: Congestion Avoidance; Fairness; TCP; Restless Bandits, Marginal Pro-ductivity Index; Economic Value.R´esum´eDans cet article nous analysons le “trade-off” entre les couˆts d’admission et lesrevenus des flots TCP Tahoe qui comp´etitionnent pour de l’espace tampon. Puisquel’espace tampon est une ressource rare lors des situations de congestion, il est im-portant de comprendre dans quelles circonstances il est optimal de se d´ebarasser despaquets. Nous d´eveloppons un mod`ele de “restless bandit” pour ´evaluer la valeur´economique des paquets dans les routeurs. Ensuite, nous utilisons l’argument que lavaleur ´economique du r´eseau augmente si les paquets avec des valeurs inf´erieures sontd´elest´es en premier ou marqu´es dans des m´ecanismes pour ´eviter la congestion. Ons’attend a ce que ces changements nous am`enent a moins de d´elais et plus de d´ebit.Acknowledgments: This research has been supported in part by the SpanishMinistry of Education and Science under grant MTM2004-02334 and an associatedPostgraduate Research Fellowship, by the Autonomous Community of Madrid-UC3Mthrough grant UC3M-MTM-05-075, and by the European Union’s Network of Excel-lence Euro-NGI. This work was mostly done during the stay of Jacko at GERAD.